Accretion disk of a white hole*

Abstract A white hole is simply a region of spacetime described by general relativity. Black holes are often assumed to form through star collapses. Based on such an assumption, the white hole region does not present. Recent research on quantum gravity indicates that a black hole must convert into a white one to avoid the singularity difficulty encountered in general relativity. If such a theory is true, it is important to ask how white holes can be observed. Anything inside a white hole must be pushed outside. However, if a white hole is empty, nothing will escape from it. We can only observe the interaction behavior between the objects falling outside and the white hole. In this paper, we observe that the structure of the accretion disk around a white hole is exactly the same as the one around a black hole. The only possibility to distinguish a white hole from a black one is the light passing through the white hole. The image properties of white holes for such scenarios are investigated in this paper. Based on our analysis and current observation facts, we cannot certainly determine if M87 and Sgr A* are black or white holes.